Daptomycin In Vitro Activity against Methicillin-Resistant Staphylococcus aureus Is Enhanced by d-Cycloserine in a Mechanism Associated with a Decrease in Cell Surface Charge.

The killing activity of daptomycin against an isogenic pair of daptomycin-susceptible and daptomycin-nonsusceptible (DNS) methicillin-resistant Staphylococcus aureus (MRSA) strains was enhanced by the addition of certain cell wall agents at 1× MIC. However, when high inocula of the DNS strain were used, no significant killing was observed in our experiments. Cytochrome c binding assays revealed d-cycloserine as the only agent associated with a reduction in the cell surface charge for both strains at the concentrations used.

Utility of peptide nucleic acid fluorescence in situ hybridization for rapid detection of Acinetobacter spp. and Pseudomonas aeruginosa.

The utility of peptide nucleic acid fluorescence in situ hybridization (PNA FISH) for the detection of Acinetobacter spp. and Pseudomonas aeruginosa was evaluated on broth suspensions and spiked blood cultures of ATCC strains and clinical isolates with select gram-negative rods. After testing 60 clinical isolates, PNA FISH had a sensitivity and specificity of 100% and 100%, respectively, for Acinetobacter spp. and 100% and 95%, respectively, for P. aeruginosa. PNA FISH was able to detect both pathogens simultaneously and directly from spiked blood cultures.

Studies on antibiotic syngerism against enterococci. II. Effect of various antibiotics on the uptake of 14 C-labeled streptomycin by enterococci.

The mechanism by which agents that inhibit bacterial cell wall synthesis produce a synergistic effect against enterococci when combined with aminoglycoside antibiotics has not been elucidated. Using (14)C-labeled streptomycin, it could be shown that uptake of this aminoglycoside antibiotic was markedly enhanced in enterococci growing in the presence of penicillin or other agents which inhibit the synthesis of bacterial cell walls. There was no enhancement of streptomycin uptake when the cells were incubated with antibiotics which primarily affect the bacterial cell membrane or inhibit protein synthesis. Increased streptomycin uptake was produced by penicillin only in actively growing bacteria. These observations are consistent with the hypothesis that enterococci exhibit a natural barrier to the entry of streptomycin which can be overcome by agents which inhibit cell wall synthesis, thus producing a synergistic effect.

Aminoglycoside-inactivating enzymes in clinical isolates of Streptococcus faecalis. An explanation for resistance to antibiotic synergism.

Clinical isolates of enterococci (Streptococcus faecalis) with high-level resistance to both streptomycin and kanamycin (minimal inhibitory concentration >2,000 mug/ml), and resistant to synergism with penicillin and streptomycin or kanamycin were examined for aminoglycoside-inactivating enzymes. All of the 10 strains studied had streptomycin adenylyltransferase and neomycin phosphotransferase activities; the latter enzyme phosphorylated amikacin as well as its normal substrates, such as kanamycin. Substrate profiles of the neomycin phosphotransferase activity suggested that phosphorylation occurred at the 3'-hydroxyl position, i.e., aminoglycoside 3'-phosphotransferase. A transconjugant strain, which acquired high-level aminoglycoside resistance and resistance to antibiotic synergism after mating with a resistant clinical isolate, also acquired both enzyme activities. Quantitative phosphorylation of amikacin in vitro by a sonicate of the transconjugant strain inactivated the antibiotic, as measured by bioassay, and the phosphorylated drug failed to produce synergism when combined with penicillin against a strain sensitive to penicillin-amikacin synergism.No differences were found in the sensitivity of ribosomes from a sensitive and resistant strain when examined in vitro using polyuridylic acid directed [(14)C]-phenylalanine incorporation in the presence of streptomycin, kanamycin, or amikacin. Therefore, we conclude that aminoglycoside-inactivating enzymes are responsible for the aminoglycoside resistance, and resistance to antibiotic synergism observed in these strains.

Plasmid-mediated resistance to antibiotic synergism in enterococci.

Mating experiments have shown that high-level resistance (minimal inhibitory concentration greater than 2,000 microgram/ml) to streptomycin and kanamycin, and resistance to penicillin-streptomycin and penicillin-kanamycin synergism are transferable by conjugation from resistant clinical isolates of enterococci to a sensitive recipient strain. Cesium chloride-ethidium bromide ultracentrifugation revealed a satellite (plasmid) band in resistant clinical isolates and the transconjugant strains but not in the sensitive recipient. Examination of these satellite bands by agarose gel electrophoresis and electron microscopy demonstrated a common plasmid with a weight of 45 megadaltons. Novobiocin treatment of a resistant clinical isolate produced simultaneous loss of high-level resistance to streptomycin and kanamycin, and of resistance to penicillin-aminoglycoside synergism. These results suggest that (a) high-level resistance to streptomycin and kanamycin among some clinical isolates of enterococci is associated with a 45 megadalton plasmid, and (b) the same plasmid is also responsible for the resistance to penicillin-aminoglycoside synergism observed in these strains.

Treatment of vancomycin-resistant Enterococcus faecium infections with quinupristin/dalfopristin.

Clinicians caring for patients with vancomycin-resistant Enterococcus faecium (VREF) infections face severe constraints in the selection of treatment. Quinupristin/dalfopristin (Synercid) is active in vitro against VREF, with a MIC(90) of 1.0 microg/mL. We investigated the clinical efficacy and safety of this agent in a multicenter, prospective, noncomparative, emergency-use study of 396 patients. Patients were included if they had signs and symptoms of active infection, including bacteremia of unknown origin, intra-abdominal infection, and skin and skin-structure infection, with no alternative antibiotic therapy available. The mean duration of treatment was 20 days (range, 4-40 days). The clinical response rate was 68.8% in the evaluable subset, and the overall response rate was 65.6%. The most common adverse events related to quinupristin/dalfopristin were arthralgias and myalgias. Related laboratory abnormalities were rare. In this severely ill patient population, quinupristin/dalfopristin was efficacious and demonstrated an acceptable safety profile in the treatment of VREF infection.

Infections with Acinetobacter calcoaceticus (Herellea vaginicola): clinical and laboratory studies.

In a retrospective review of 53 patients, 58 episodes of infection due to Acinetobacter calcoaceticus var. anitratus (Herellea vaginicola) were studied. Although the organism is widely distributed in nature, it is of relatively low virulence since colonization is more frequently noted than infection and since most infections occur in patients subjected to the epidemiologic pressures common to nosocomial, gram-negative bacillary infection: prior antibiotic therapy; instrumentation and manipulation (e.g., endotracheal intubation, urinary bladder catheterization, arterial and venous cannulation); surgery; hospitalization, especially with residence in an intensive care unit; severe underlying disease, either systemic (e.g., chronic obstructive pulmonary disease, malignancy) or localized to the infected area (e.g., prior bacterial or aspirational pneumonia, trauma). Pneumonia was the most common infection due to A. calcoaceticus, and occurred only in patients with a tracheostomy or endotracheal tube in place. In over half the 25 patients, more than one lobe was involved and bronchopneumonia was the usual roentgenographic appearance. Cavitation (2 patients) and empyema formation (3 patients) were uncommon. The severity of acinetobacter pneumonia is reflected in the high mortality rate (44% overall, with a 36% mortality rate due primarily to infection). Tracheobronchitis due to A. calcoaceticus was less severe than pneumonia since no patients died primarily as a result of the infection. Urinary tract infections occurred in five patients, none of whom were ill and none of whom died. Urinary bladder catheterization was thought to be responsible for infection in three patients, and in at least four of the five patients infection was restricted to the lower tract. Wound infections were noted in six patients who had undergone surgery and were related to the presence of foreign bodies in the operative site in five of the patients. Surgical debridement and/or drainage of the infected area was the primary therapeutic measure employed in most cases. Only one patient died and this was a result of noninfectious causes. Skin infection due to A. calcoaceticus was seen in two patients, one of whom exhibited fulminant, fatal cellulitis and septicemia in the setting of pancytopenia. All nine patients with acinetobacter septicemia had received antecedent antibiotic therapy, and in all cases intravenous catheters were in place at the time bacteremia occurred. Clinically, seven of the nine patients were in shock. The mortality rate was 44% overall, with a 22% mortality rate due to infection. Although septicemia was thought to be "line-related" in five of the nine patients, serious post-bacteremic complications developed in three patients: prosthetic valve endocarditis, suppurative thrombophlebitis and subhepatic abscess.

Have the new beta-lactams rendered the aminoglycosides obsolete for the treatment of serious nosocomial infections?

Hospital-acquired infections are often due to multi-resistant gram-negative bacilli. When treating these infections, the physician must use potent antibiotics that have broad spectrums of activity. Aminoglycosidic aminocyclitols and the newer beta-lactam antibiotics are particularly valuable in the management of hospital-acquired infections. This article discusses the role of both classes of antibiotics in this setting.

Rationale for use of antimicrobial combinations.

In most cases antimicrobial combinations are employed to broaden the spectrum of coverage. This clinical application is likely to be successful as long as the combinations are not antagonistic. Most examples of antibiotic antagonism are those in which a bacteriostatic agent renders a bactericidal agent "static." Another type of antagonism occurs when cefoxitin (which has a propensity to induce beta-lactamase production) is combined with another beta-lactam antibiotic. Combination drug therapy prevents emergence of resistant strains in mycobacterial infections and in infections due to methicillin-resistant staphylococci and certain other resistant organisms. Synergistic combinations should allow the use of lower concentrations of drugs in combination and thus diminish the incidence of dose-related antibiotic toxicity, but the concept has met with only limited success so far. Three types of antimicrobial combination or interaction result in enhanced (synergistic) antimicrobial activity. These types include combinations of agents that inhibit bacterial cell wall synthesis with aminoglycosidic aminocyclitols, the use of beta-lactamase inhibitors in combination with beta-lactam antibiotics, and the administration of agents that act on sequential steps in one of the bacterial metabolic or synthetic pathways. Combinations of two beta-lactam antibiotics that bind to complementary penicillin-binding proteins may represent an analogous situation. Amdinocillin binds specifically to penicillin-binding protein 2, and in vitro studies have clearly demonstrated synergism when amdinocillin is combined with other penicillins and cephalosporins that have higher affinity for other penicillin-binding proteins.

Can the third-generation cephalosporins eliminate the need for antimicrobial combinations?

Antimicrobial combinations have been widely utilized since the beginning of the chemotherapeutic era. This is true despite the fact that the use of such combinations has a number of potential disadvantages, including (1) antibiotic antagonism; (2) an increased incidence of toxicity; (3) the emergence of multi-resistant organisms; (4) promotion of a false sense of security; and (5) increased expense. The reasons generally given for the use of such combinations include (1) antimicrobial synergism, (2) suppression of antimicrobial resistance, (3) decreased toxicity, and (4) broader coverage. Although there are clearly some situations in which synergistic combinations have been shown to be useful (such as in the treatment of enterococcal endocarditis and severe Pseudomonas infections), the use of combination therapy to reduce the emergence of resistance (excluding the treatment of mycobacterial infections and of infections in which rifampin is used) or to reduce toxicity has not met with widespread success. Indeed, most combinations are used simply to broaden the spectrum of antimicrobial coverage. The development of new penicillins and cephalosporins with broader spectra of activity has raised the distinct possibility that these drugs could be used as single agents for the treatment of most serious infections. Although comparative studies performed to date suggest that the new broad-spectrum penicillins and cephalosporins may be useful as single agents in the treatment of infections in a variety of clinical situations in which combinations are now commonly employed, additional studies enrolling greater numbers of patients are necessary to determine whether these agents can replace combination therapy. The use of single-drug therapy in the management of febrile episodes and documented infections in neutropenic patients remains problematic because of the greater likelihood of infections with organisms such as Pseudomonas aeruginosa, in which case combination therapy is often required. Earlier studies have clearly documented that combinations of antibiotics that are synergistic are more effective in treating bacteremias and other serious infections in neutropenic patients than are combinations that have failed to demonstrate synergism. Because of the increased activity of some of the newer drugs, such as ceftazidime, against P. aeruginosa it is possible that such agents could be used as monotherapy for patients with severe neutropenia. This possibility is an attractive one, but it should be studied carefully to make certain that it will not be associated with significant failure due to the emergence of resistant organisms.

The specter of glycopeptide resistance: current trends and future considerations.

Two glycopeptide antibiotics, vancomycin and teicoplanin, are currently available for clinical use in various parts of the world, whereas a third, avoparcin, is available for use in agricultural applications and in veterinary medicine in some countries. Because of their outstanding activity against a broad spectrum of gram-positive bacteria, vancomycin and teicoplanin have often been considered the drugs of "last resort" for serious infections due to drug-resistant gram-positive pathogens. Glycopeptides had been in clinical use for almost 30 years before high-level resistance, first reported in enterococcal species, emerged. More recently, there have been disturbing reports of low- and intermediate-level resistance to vancomycin in strains of Staphylococcus aureus. A review of earlier reports reveals, however, that S. aureus strains with reduced susceptibility to glycopeptides were first identified >40 years ago. Such strains may occur in nature or may have developed low-level mutational resistance in response to the selection pressure of glycopeptide therapy. Of considerably greater concern is the possibility that vancomycin resistance genes found in enterococci may be transferred to more virulent organisms such as staphylococci or Streptococcus pneumoniae.

Clinical, microbiologic and therapeutic aspects of purulent pericarditis.

Twenty-six patients with purulent pericarditis were seen at the Massachusetts General Hospital between 1960 and 1974. The diagnosis was made in 18 of them during life, but only 6 survived, with an over-all mortality rate of 77 per cent. In eight patients, purulent pericarditis developed in the early postoperative period after thoracic surgery. In seven, purulent pericarditis was the result of contiguous spread of infection from a pleural, mediastinal or pulmonary focus in nonsurgical patients. In five patients, it was the result of direct spread to the pericardium from an intracardiac infection. In the remaining six patients, purulent pericarditis developed as the result of a systemic bactermia. Immunosuppressive therapy, extensive thermal burns, lymphoproliferative disease and other systemic processes affecting host resistance were present in at least half the patients. Staphylococcus aureus was the etiologic agent in the largest number of patients (8 of 26 in this report). However, in contrast to previous studies, in a significant number of the patients (five), purulent pericarditis was the result of fungal infection (in three patients subjected to thoracic surgery and in two immunosuppressed patients). This report confirms that purulent pericarditis is an acute disease with a fulminant course. The diagnosis is easily missed since classic signs of pericarditis (including chest pain, friction rub and diagnostic electrocardiographic abnormalities) may be absent. The echocardiogram shows considerable promise in allowing earlier diagnosis of the pericardial effusion which accompanies purulent pericarditis. Optimal therapy consists of prolonged antibiotic therapy and aggressive drainage of the pericardium. In this series, there were 6 survivors among the 11 patients (55 per cent) who received appropriate therapy.

Antimicrobial combinations in the therapy of infections due to gram-negative bacilli.

Antimicrobial combinations are used most frequently to provide broad-spectrum coverage; however, they are also frequently employed to enhance antimicrobial activity (synergism). Although there is extensive in vitro documentation of synergism for many antibiotic combinations, a clear advantage for these combinations has been difficult to demonstrate in clinical studies. Several types of combinations have been useful in clinical medicine and frequently result in synergism. These include combinations of a cell wall-active agent with an aminoglycosidic aminocyclitol, combinations of a beta-lactamase inhibitor with a beta-lactam, and combinations of agents that inhibit sequential steps in a metabolic pathway. Given its spectrum of activity, aztreonam will often be used with clindamycin or a beta-lactam antibiotic. Combinations of beta-lactams may be synergistic via several mechanisms. However, these combinations also exhibit significant potential for antagonism when used against gram-negative bacilli and, therefore, require careful evaluation prior to clinical use.

Beta-lactam/aminoglycoside combinations: interactions and their mechanisms.

Combinations of beta-lactams with aminoglycosides are widely used in the therapy of infections. There are a number of theoretic advantages to using such combinations. Indeed, combinations of beta-lactams and aminoglycosides usually result in synergism or indifference and very rarely in antagonism. The mechanisms of synergism, resistance to synergism, and antagonism have been studied extensively in enterococci; further studies are necessary to define such mechanisms in other organisms.

Hemophilus influenzae in hospitalized adults: current perspectives.

In an eight year period 16 cases of serious extrapulmonary Hemophilus influenzae infection in adults were identified, including cases of meningitis, pericarditis, epiglottitis, empyema, cellulitis, osteomyelitis, endometritis, urinary tract infection, orbital cellulitis, primary peritonitis, mesenteric lymphadenitis and aortic graft infection. An 18 month prospective study of H. influenzae infection in hospitalized adults identified 10 cases of bronchitis, 25 of pneumonia and 65 of respiratory tract colonization, but there were no extrapulmonary infections. In 29 percent of the respiratory tract infections, H. influenzae appeared to be a nosocomial pathogen; in 71 percent, the infection was mixed. Finally, 110 clinical isolates of H. influenzae were studied for antimicrobial susceptibility. Eight percent were ampicillin resistant, two strains were resistant to tetracycline and one to chloramphenicol, but all were susceptible to trimethoprim-sulfamethoxazole and cefamandole.

Diphtheroid prosthetic valve endocarditis. A study of clinical features and infecting organisms.

The clinical features of 19 patients with prosthetic valve endocarditis due to diphtheroids were studied. Infection was noted within 60 days of cardiac surgery in 12 (63 percent) patients. Prosthetic dysfunction and infection of the valve annulus was common (74 percent). Agar dilution minimal inhibitory concentrations for 18 diphtheroids isolated from patients with prosthetic valve endocarditis indicated that 88 percent were susceptible to gentamicin, amikacin, streptomycin, erythromycin and tetracycline; all strains were susceptible to vancomycin. In time-kill studies vancomycin was highly bactericidal as was gentamicin for susceptible strains. For gentamicin-susceptible strains, penicillin-gentamicin combinations were synergistic regardless of the susceptibility of the strains to penicillin. Bactericidal synergy of penicillin-gentamicin combinations was not seen with gentamicin-resistant strains. The biochemical and physiologic features of 20 strains were studied; with the exception of colonial morphology, 18 strains were found to be similar. Four strains were classified as belonging to the group JK by the Center for Disease Control (CDC) and 14 other strains fulfilled CDC criteria for group JK diphtheroids. A technique and criteria for single disc diffusion susceptibility testing are suggested.

Resistance to gentamicin, tobramycin and amikacin among clinical isolates of bacteria.

Susceptibility to the administration of gentamicin, tobramycin and amikacin was determined for all isolates of aerobic and facultative gram-negative bacilli submitted for testing to the clinical bacteriology laboratory of the Massachusetts General Hospital between July 1, 1974, and June 30, 1976. In this 24-month period more than 46,000 isolates of bacteria were tested by the single-disc diffusion (Bauer-Kirby) method. Resistance to one or more of the aforementioned aminoglycosidic aminocyclitol antibiotics was found among 4,114 stains. Correlation with quantitative susceptibility test methods revealed that disc-diffusion methods using 10 microng discs accurately predicted resistance to gentamicin and tobramycin, but overestimated the prevalence of resistance to amikacin by 20 to 60%. Most of the gentamicin-resistant Enterobacteriaceae in this study were also cross-resistant to tobramycin but were susceptible to amikacin. Many gentamicin-resistant strains of Ps. aeruginosa were susceptible to both tobramycin and amikacin. Resistance to amikacin tended to be of relatively low magnitude (most had minimal inhibitory concentrations (MIC's) between 31 and 125 microng/ml), but organisms which were resistant to the administration of amikacin were usually resistant to the other two aminoglycosidic antibiotics as well.

Vancomycin prophylaxis in cardiac operations: determination of an optimal dosage regimen.

Vancomycin is thought to be an acceptable alternative prophylactic antibiotic to the cephalosporins in penicillin allergic patients undergoing cardiopulmonary bypass. We studied the pharmacokinetics of vancomycin in 10 patients undergoing cardiopulmonary bypass. Our results suggest that the commonly used 500 mg dose (7 mg/kg) of vancomycin given preoperatively may provide serum concentrations during cardiopulmonary bypass which are not bactericidal for many S. epidermidis strains. Thus we believe that a higher initial dose, at least 15 mg/kg, should be given.

Cephalothin prophylaxis in cardiac valve surgery. A prospective, double-blind comparison of two-day and six-day regimens.

A prospective, double-blind study comparing a 6 day with a 2 day regimen of cephalothin prophylaxis was conducted among 200 patients undergoing prosthetic valve replacement. No cases of endocarditis occurred during the 2 month follow-up. Sternal wound infection developed in 2.8 per cent of the 6 day group and 2.1 per cent of the 2 day group. Pneumonia developed in 8.5 per cent of the 6 day and 5.3 per cent of the 2 day group; most of the bacteria isolated were susceptible to cephalothin. Urinary tract infection developed more frequently in the 2 day group (17.0 versus 8.5 per cent), particularly during the first 6 postoperative days. Three of 11 patients with no detectable cephalothin in their sera at the close of operation developed staphylococcal wound infections, compared with 2 of 175 patients whose sera contained cephalothin at the close of surgery (p = 0.002, Fisher's exact test). A short course of prophylactic antibiotics is prudent, but there is no justification for prolonging their administration.

Effects of penicillin and lysozyme on the immunofluorescent and precipitin reactivity of group D streptococci.

Damage to the cell wall by growth in the presence of penicillin or by treatment with lysozyme enhanced the immunofluorescent (fluorescent antibody, FA) reactivity to group D streptococci. The optimum concentration and time of treatment with lysozyme varied inversely with the initial FA reactivity of the strain. Speciation of the organisms by a series of biochemical and physiologic tests suggested that the differences in initial FA reactivity were species-related. Thus, S. faecalis strains were the most FA-reactive and most sensitive to lysozyme. S. faecium strains were less FA-reactive and lysozyme-sensitive. S. bovis strains proved to be least FA-sensitive and were most resistant to lysozyme. Treatment with lysozyme was also effective in preparing extracts of group D antigen from all three species for Lancefield grouping by the precipitin test. The lysozyme extracts, moreover, produced much stronger reactions than those made from comparable volumes of cells by the methods of Lancefield or of Rantz and Randall.